1. Field of the Invention
The present invention generally relates to a method of manufacturing a recording medium. The present invention particularly relates to the method of manufacturing a magnetic recording medium for use in a magnetic recording and reproduction device serving as external storage device of computers.
2. Description of the Related Art
Recently, there is an increasing need for high-density recording in magnetic storage devices known as hard-disk device. In such a hard-disk device for high-density recording, it is necessary to reduce the magnetic spacing, which is a space formed between a magnetic head provided in the magnetic disk device and the surface of a magnetic disk serving as a recording medium in the main body of the hard-disk device, as much as possible. In other words, the gap between the magnetic head and the magnetic disk surface, scanned by the magnetic head, should be as small as possible. Recently, a spacing of about 50 nm or less is used.
FIG. 1 is a schematic diagram showing a magnetic disk device 100 including a magnetic head 20 and a rotating magnetic disk 10 of the related art. FIG. 1 is illustrated in an enlarged view, so as to clearly show the layered structure of the magnetic disk 10 and a magnetic spacing S.
Referring to FIG. 1, the magnetic disk has a structure including a substrate 11, an underlayer 13 formed on the substrate 11, and a magnetic layer 15 formed on the underlayer 13. A protection layer 17 of amorphous carbon is provided further on the magnetic layer 15. Further, a lubrication layer 19 of a fluorocarbon compound is formed on the protection layer 17.
As described above, in such a hard-disk device designed for high-density recording, there is a need to reduce the size of the magnetic spacing S as much as possible. On the other hand, such a reduction of the spacing S invites an increased chance that the magnetic head 20 hits the surface of the magnetic disk 10 during the operation of the hard-disk device 100. In view of the situation noted above, it is preferable to smooth the surface of the magnetic disk 10 as much as possible. Further, technical improvement is required, such as a reduction in thickness of the magnetic disk 10.
The magnetic disk device 100 described above generally operates in accordance with the so-called contact-start-stop (CSS) mode. With the CSS mode, a lift surface 20a of the magnetic head 20 contacts and slides over the surface of the magnetic disk 10 at the start or stop phase of rotation of the magnetic disk 10. On the magnetic disk 10, for the CSS-mode operation, it should be noted that friction and abrasion of the disk surface primarily depends on the nature of the protection layer 17 and the lubrication layer 19. Thus, the protection layer 17 and the lubrication layer 19 are important for maintaining the reliability of the magnetic disk device 100. Particularly, due to the recent trend of technology to reduce the spacing between the floating magnetic head and the magnetic layer 15 carrying a high-density record of information, there is a need for maintaining stable friction and abrasion properties for the lubrication layer 19 over a longer period of time.
FIGS. 2A to 2F are diagrams showing various steps of manufacturing the magnetic disk 10 according to the related art. Referring to FIG. 2A, a non-magnetic substrate 11 of a material such as Al plated with NiP is prepared. Next, in the step of FIG. 2B, very small irregularities, or textures, are formed on the non-magnetic substrate 11. Next, in the step of FIG. 2C, a deposition process, such as a sputtering process is implemented, and an underlayer 13 of a Cr alloy, a magnetic layer 15 of a Co alloy, and a protection layer 17 of amorphous carbon are deposited consecutively on the substrate 11. Then, in the step of FIG. 2D, a pre-heat treatment is applied to the structure obtained in the step of FIG. 2C. A lubrication layer 19 of fluorocarbon compound is uniformly applied to the surface of the protection layer 17 in FIG. 2E by dipping the structure of FIG. 3D into a solution of the fluorocarbon compound. After the lubrication layer 19 has been thus formed, a heating process or UV (ultraviolet beam) curing process is implemented in the step of FIG. 2F for curing the fluorocarbon lubrication layer 19. As a result of the curing process of FIG. 2F, it should be noted that the proportion of the lubrication layer 19 bonded firmly to the surface of the protection layer 17 is increased. The part of the lubrication layer 19 bonded to the surface of the layer 17 is hereinafter referred to as a bonding layer part.
Meanwhile, when the surface of the magnetic disk 10 is entirely smooth and flat, there will be an increase in the contact area between the magnetic head 20 and the magnetic disk 10. Thus, in order to prevent a part of lubrication layer from being taken away and transferred to the magnetic head 20 under the situation noted above, it is preferable to provide the lubrication layer 19 with a small thickness of about 1 to 2 nm.
As has been described above, there have been various efforts made on the lubrication layer 19 substantially serving as the surface of the magnetic disk 10. Such efforts include reducing the thickness of the lubrication layer 19 and improving the bonding strength between the lubrication layer 19 and the protection layer 17. In relation to increases in data transfer rates between a hard disk drive and the computer, and further in relation increases in the recording densities the rotational speed of the magnetic disk 10 is also increasing. Presently, a considerably high speed of about 7,200 to 10,000 rpm is used in the advanced high-density hard disk devices. It should be noted that such high rotational speed of the magnetic disk 10 results in an increased centrifugal force. Thus, there is a tendency, in the lubrication layer 19 of the related art, for the part of the layer 19 not bonded to the surface of the protection layer 17 to undergo spin off as a result of the large centrifugal force. The proportion of the unbonded part, or a so-called mobile layer part, of the lubrication layer 19 reaches as much as 50% to 70%. As a result of the spin-off of the mobile layer part 19, the thickness of the lubrication layer 19 can be reduced to as small as only a few .ANG.ngstroms, while such an extreme thinning of the lubrication layer 19 is problematic in that a stable lubrication functions of the layer 19 cannot be guaranteed over a long period of time.
In view of the need for reducing the friction force of the magnetic head 20 against the above-described magnetic disk 10 in the CSS mode operation of the hard disk device, recent hard disk technology tends to use very small protrusions on the lift surface 20a of the magnetic head and/or on the CSS region (not shown) of the magnetic disk 10. While such a structure may be useful for reducing the friction, there arises a in that the pressure between the magnetic disk surface and the magnetic head will increase in correspondence to the contacting part as compared with the structure where the lift surface 2a and/or the CSS region are/is flat. Therefore, with the lubrication layer 19 of the magnetic disk 10 of the related art, the lubrication layer 19 may break due to the contact and sliding of the magnetic head 20. Accordingly, this poses a problem in that the protrusions may be worn down within a short period of time, thus causing an increased aberration.
In order to solve the problem described above, it is certainly possible to provide the lubrication layer 19 with an increased thickness. However, with the related art, the amount of the bonding layer part bonded to the protection layer 17, by the heating or UV curing process (see FIG. 2F), is not sufficient. In other words, there is still a considerable amount of mobile layer part included in the lubrication layer 17. This mobile layer part 8 will spin off as a result of the high-speed rotation of the magnetic disk 10, and the thickness of the lubrication layer 19 will be reduced with time, thus resulting in the problem described above. Further, the foregoing approach to increase the lubrication layer initial thickness causes other problems. For example, a part of the lubrication layer 19 may be transferred to the lift surface 20a of the magnetic head 20, or the distance between the magnetic head 20 and the surface of the magnetic disk 10 becomes too large for the desired high-density recording.